2003;51:649\655. that these populations may be one and the same. Therefore, the aim of this study was to determine whether there is a difference between the classical RF and regRF. Methods Classical RF was measured in diseased blood by the latex fixation method, and regRF was detected by the agglutination of human IgG\loaded tanned erythrocytes. Competitive analysis was used to determine the specificity of rheumatoid factors. Results It was found that regRF and pathology\associated RF constitute different antibody populations. Pathology\associated RF is specific for lyophilized IgG. RegRF does not interact with IgG. RegRF is usually specific to conformers of IgG Fc fragments that have a reduced hinge. In latex\positive rheumatoid arthritis sera, regRF may be present in addition to pathology\associated RF. The latex fixation method detects both rheumatoid factor populations. Conclusion RegRF and classical pathology\associated RF have different specificity. test. 3.?RESULTS 3.1. RegRF in latex\positive diseased serum Sera taken from patients diagnosed with rheumatoid arthritis as well as from patients GW438014A being examined after presenting with complaints of joint pain and swelling were tested for rheumatoid factor by the latex fixation method. Sera found to be latex\positive were selected. Most (77%) of the sera selected had been obtained from patients with an established rheumatoid arthritis diagnosis, made using EULAR diagnostic criteria. The remaining latex\positive sera were from patients complaining of joint pain who did not yet have a diagnosis. Hereinafter, the latex\positive sera obtained from both rheumatoid arthritis patients and from as\yet undiagnosed patients are referred to as latex\positive diseased sera (Physique?1A). In the experiments where sera only from diagnosed rheumatoid arthritis patients were used, the sera are referred to as rheumatoid arthritis sera. Open in a separate window Physique 1 Agglutination of tanned IgG\loaded erythrocytes and IgG\coated latex particles by patient sera. A, Agglutination of tanned IgG\loaded erythrocytes by healthy sera and latex\positive patient sera. The results are presented as means??SD. *Statistically significant in relation to group ++, test). B, Correlation analysis Latex\positive diseased sera and latex\unfavorable healthy sera were studied by GW438014A agglutination of tanned IgG\loaded erythrocytes. It was found that both diseased and healthy sera cause agglutination of tanned IgG\loaded erythrocytes. Comparison of the intensity of the latex fixation reaction with that of the tanned IgG\loaded erythrocyte agglutination reaction induced by diseased sera showed that the higher the activity of diseased sera in the latex test, the higher the average RF level detected in the sera by the tanned IgG\loaded erythrocyte agglutination method (Physique?1A). However, individual analysis showed that in diseased sera assigned to the same group based on the intensity of the latex fixation they induced, the titers detected by the agglutination of tanned IgG\loaded erythrocytes vary significantly. In the +++ KIAA1836 group (latex test), about GW438014A 40% of sera had a relatively low titer in the tanned loaded IgG erythrocyte agglutination reaction (from 1:32 to 1 1:128), comparable to the titer of sera from the + and ++ groups (latex test). This suggests that in diseased serum, in addition to the RF detected by tanned IgG\loaded erythrocyte agglutination, there are other antibodies detectable only by latex fixation. In some latex\positive diseased sera, the RF titer was measured by latex fixation and then compared with the RF level measured by the agglutination of tanned IgG\loaded erythrocytes. Correlation analysis did not reveal a significant relationship between the RF level revealed by the agglutination of tanned IgG\loaded erythrocytes and the RF level revealed by latex fixation (k?=?0.64) (Physique?1B). Thus, latex\positive diseased sera induce agglutination of tanned IgG\loaded erythrocytes. However, the RF level.